Prior to weaving glass fibers into a fabric, the fibers are typically coated with a starch-oil size which protects the fibers from abrasion, binds them together and also serves as a lubricant during processing. The size is typically compounded of dextrinised or amylose starches, hydrogenated vegetable oils, waxes, emulsifiers, film formers and wetting agents, the precise composition varying depending on the manufacturer and processing conditions. Typical fiber glass size compositions and application techniques are disclosed, for example, in U.S. Pat. No. 3,227,192.
When the glass fabric is to be used as a reinforcing material in, for example, plastic laminates, by combining the fabric with thermosetting or thermoplastic resins, the fabric is typically first coated with a bonding material such as an organo-silane coupling agent which provides a stable bond between the glass and the resin. The presence of the size on the fiber used to weave the fabric prevents effective adhesion of the glass fabric with the coupling agent and consequently the size must be substantially completely removed from the fabric before the coupling agent is applied to the fabric.
Size is typically removed from glass fabric by heating the fabric at an elevted temperature for a time sufficient to burn-off the size. Typically, the glass fabric is subjected to from 72 to 96 hours of heat treatment at a temperature of about 800.degree. F. to 900.degree. F. Although the heat treatment is effective in removing the size, it is disadvantageous from the standpoints of both time and energy consumption. More importantly, such heat treatment results in a substantial reduction in tensile strength of the fabric. Although the loss in tensile strength is not particularly serious if the glass fabric is intended for use as a decorative material, for example, draperies and the like, the considerable loss in tensile strength is a definite disadvantage when the glass fabric is to be used as a reinforcing material in plastic laminates.
In addition, the woven fabric is typically spotted and smudged with machine oil and grease picked up from the weaving apparatus. During high temperature heat treatment, the oil and grease picked up by the fabric during the weaving operation is converted to hydrochloric acid which attacks and erodes the fabric, and studies have shown that as much as 5 percent of the fabric is thus rendered unsuitable for use.
Chemical desizing methods are also known and described, for example, in U.S. Pat. No. 3,990,908 and U.S. Pat. No. 3,019,140 which respectively disclose desizing by oxidation and solvent treatment.